Compact, high efficiency, high isolation power amplifier

ABSTRACT

A power feedforward amplifier uses integral cavities to provide RF isolation between subcircuits of the power amplifier. The chassis includes a main chassis body and a lid structure adapted to couple with the chassis body and define the subcircuit cavities. The inner lid includes an amplifier dividing wall and interstage walls adapted to isolate the main and error amplifier subcircuits of the feedforward power amplifier and further to isolate individual components of the subcircuits. In one embodiment, the amplifier subcircuits are mounted on a single circuit board and isolated from each other by the dividing wall. A delay line subcircuit portion is integral with the main chassis body and is coupled beneath the error amplifier subcircuit to contain and electromagnetically shield a delay line filter subcircuit while providing direct connection with the error amplifier.

RELATED APPLICATIONS

This application is a Divisional Application of U.S. application Ser.No. 10/085,200 filed Feb. 26, 2002 now U.S. Pat. No. 6,760,230, which inturn claims the filing benefit and priority of U.S. ProvisionalApplication, entitled “Compact Low Cost High Isolation Amplifier Chassisand Method of Manufacturing the Same,” Ser. No. 60/272,013, filed Feb.28, 2001, each application of which is incorporated herein by referencein its entirety.

FIELD OF THE INVENTION

The present invention relates generally to power amplifiers andspecifically to a compact, high efficiency, and high isolation poweramplifier.

BACKGROUND OF THE INVENTION

Ideally, a radio frequency (RF) power amplifier would be perfectlylinear, and thereby faithfully reproduce amplified RF signals. Inpractice, RF power amplifiers are generally non-linear and add a certainamount of unwanted distortion to the amplified signal. This distortionof the amplified signal is realized as one or more intermodulationdistortion (IMD) products which are undesirable in the amplified outputsignal. Therefore, it is desirable to reduce or generally eliminate suchIMD products and other error from the amplified signal.

Several techniques have been developed to reduce IMD products inamplified RF signals, such as, for example, feedforward amplification.One type of single-loop, feedforward power amplifier uses a mainamplifier subcircuit, a delay line filter subcircuit, and an erroramplifier subcircuit. In the operation of the feedforward amplifier, themain amplifier subcircuit amplifies an input carrier, therebyintroducing non-linearity error in the form of IMD products. The delayline filter subcircuit receives the input carrier and the output carrierof the main amplifier subcircuit, including the introduced error. Acarrier cancellation loop incorporated within the delay line subcircuitsubtracts the input carrier from the main amplifier output carrier anderror, so that only the error signal remains. The remaining error signalis then fed into the error amplifier subcircuit, where the error isamplified and inverted by an error amplifier subcircuit. The invertederror is then subsequently combined with the delayed output carrier anderror from the main amplifier subcircuit. In that way, the invertederror signal cancels the error signal from the main amplifiersubcircuit, generally leaving only the amplified output carrierremaining. Such feedforward power amplifiers are useful with a varietyof RF transmission systems, including cellular telephone base stationsand other communication systems requiring amplification with highlinearity.

Existing designs for feedforward power amplifiers have variousdrawbacks. First, feedforward amplifiers are generally very inefficientfrom a power standpoint. For example, 5%-10% efficiency is typical. Suchinefficiency is partially the result of the delay that must beintroduced into various of the signals in the delay line subcircuit ofthe system. Such delays generally translate into heat and power losses.This is particularly true for the delay introduced in the high poweroutput of the main amplifier. For example, to achieve proper errorcancellation, delay of the output from the main amplifier subcircuitmust coincide with the output and delay of the error amplifiersubcircuit. The greater the delay introduced by the error amplifiersubcircuit, the greater the delay (and resultant power loss/efficiencyreduction) required for the output signal of the main amplifiersubcircuit. Therefore, it is always desirable in such feedforwardamplifiers to try to maximize efficiency by reducing introduced delays.

Existing amplifier designs are also complex in design, which increasestheir overall cost, not only from a material standpoint, but also fromthe manufacturing and assembly side, as well. For example, the varioussubcircuits comprising a feedforward RF amplifier must beelectromagnetically isolated from each other for proper operation. Thatis, leakage paths which allow electromagnetic signals to propagate fromone subcircuit to another must be minimized. Leakage paths may betypically minimized by surrounding each subcircuit in a Faraday shieldtype enclosure.

Several methods of maintaining the necessary isolation have been used inthe past; however, such methods have resulted in expensive complexities.In some designs, subcircuits such as the main amplifier and erroramplifier are provided in separate enclosed conductive chassis.Interconnects between the subcircuits are then provided with connectors,shielded cables, and filtered signal lines. This solution adds materialand manufacturing complexities and costs, as well as unwanted size tothe feedforward power amplifier. Because existing feedforward amplifierdesigns use several circuit boards and amplifier subcircuits, severalchassis must be constructed and connected together.

Alternatively, cavities for the various circuit boards might be machinedinto a chassis, with the boards being dropped into the cavities.However, such a design further complicates the interconnections betweenthe components of the system and between the boards.

Another isolation technique employed is the use of separate bolt-on orsoldered internal shielding walls. However, such methods for achievingisolation involve additional components, more assembly steps, andtherefore higher production costs. Still further, separate metal boxesor cans may be used to separate the subcircuits, which are then boltedinto other, larger boxes. As may be appreciated, such a design furtheradds to the complexity of the design with resulting increased materialand production costs. Further, these methods still do not always providethe level of isolation desired for feedforward amplifiers.

Furthermore, while it is desirable to also shield the delay linesubcircuit from the other components of a feedforward power amplifier,it is an additional goal to position the delay line subcircuit so as tominimize the length of connections between the delay line subcircuit andthe other circuit components, thereby reducing output losses within theamplifier, and increasing overall efficiency.

Therefore, there is a need in the art to reduce the complexity, size,and overall cost of a feedforward amplifier design while still achievingdesired efficiency and isolation characteristics in its operation. Morespecifically, there exists a need for a feedforward power amplifierdesign that provides the necessary isolation between subcircuits of thepower amplifier, maintains subcircuits of the power amplifier indesirable position with respect to one another, and provides desiredefficiency. Such goals are preferably accomplished in a design having alow material cost, a simple, low cost assembly process, and a smallsize.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description of the embodiments given below, serve toexplain the principles of the invention.

FIG. 1 is a schematic circuit diagram showing various subcircuits of afeedforward power amplifier in one embodiment of the present invention;

FIG. 2 is a perspective view of a top side of an inner lid structureaccording to one embodiment of the present invention;

FIG. 3 is a perspective view of a bottom side of an inner lid structureaccording to one embodiment of the present invention;

FIG. 3A is a perspective view of a bottom side of an inner lid structurein accordance with another embodiment of the invention;

FIG. 3B is a top plan view of a circuit board containing both the mainamplifier and error amplifier in accordance with one aspect of theinvention.

FIG. 4 is a perspective view of a main chassis body according to oneembodiment of the present invention;

FIG. 5 is a top view of a main chassis body according to one embodimentof the present invention;

FIG. 6 is a perspective view of a main chassis body according to thepresent invention housing a main amplifier and an error amplifier;

FIG. 7 is a perspective view of a main chassis body with an inner lidstructure in place according to one embodiment of the present invention;

FIG. 8 is a top view of a power amplifier chassis according to oneembodiment of the present invention; and

FIG. 9 is a cross-sectional view of a power amplifier according to oneembodiment of the present invention.

FIG. 10 is a partial cross-sectional view of a power amplifierillustrating the connection between an error amplifier subcircuit anddelay line subcircuit according to one aspect of the present invention;

FIG. 11 is a bottom view, in partial cross-section of one embodiment ofthe invention, illustrating a delay line subcircuit.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

For better understanding of the context of the disclosed embodiments ofthe present invention, a description of one suitable feedforwardamplifier design is useful, and is set forth herein for illustrativepurposes. A person of ordinary skill in the art will recognize otherdesigns as also being suitable for practicing the invention.

FIG. 1 shows a circuit block diagram of one type of feedforward poweramplifier 10 suitable for use in one embodiment of the presentinvention. Dotted lines, “A” in FIG. 1, are used to show separationbetween various subcircuits which are to be electromagnetically isolatedvia a design and chassis according to an embodiment of the presentinvention. Subcircuits shown in FIG. 1 generally include a delay linesubcircuit 12, a main amplifier subcircuit 14, an error amplifiersubcircuit 16, a forward power detector subcircuit 18, a scanningreceiver subcircuit 20, and a reverse power detector subcircuit 22. Thecircuitry and operation of the power amplifier 10 and various of thesubcircuits is described herein, though it is understood by a person ofordinary skill in the art that the present invention may be Used withlinear power amplifiers having more, or fewer, or different subcircuitsthan those shown in FIG. 1. For example, separate subcircuits asdescribed may be combined into larger subcircuits, or new subcircuitsoffering different functionality may be used. Additionally, the presentinvention may be used with feedforward amplifiers employing secondaryerror cancellation loops, or any other type of amplifier using one ormore delay lines to improve linearity.

The feedforward power amplifier 10 (which may be a multi-carrieramplifier) includes an input 100, a main signal path 102, a feedforwardpath 104, and an output 112. The power amplifier 10 further includes acarrier cancellation loop (CCL) 106, an error correction loop (ECL) 108,and a scanning receiver 144. On the feedforward path 104, whichprogresses through several subcircuits, there is provided a feedforwarddelay filter 118, a feedforward variable attenuator 120, a feedforwardphase shifter 122, and an error amplifier 124. On the main signal path102, also progressing through the subcircuits, there is provided a mainvariable attenuator 134, a main phase shifter 136, a main amplifier 138,and a main delay filter 140.

The input 100 receives radio frequency (RF) carrier signals, and aninput carrier coupler 114 couples the RF carrier signals onto both themain signal path 102 and the feedforward path 104. Alternatively, asplitter (not shown) may be used to provide the RF carrier signals ontothe main signal path 102 and the feedforward path 104.

Referring still to FIG. 1, the RF carrier signals on the main signalpath 102 may be attenuated by the main variable attenuator 134 and phaseshifted by the main phase shifter 136, although not necessarily in thatorder. A CCL (106) power detector 150, shown located in the erroramplifier subcircuit 16, may be provided on the feedforward path 104 tomonitor the power level of the signals after the carrier signals havebeen subtracted in the CCL 106. Control of the main variable attenuator134 and the main phase shifter 136 may be under microprocessor controlor any other suitable interface capable of monitoring the CCL powerdetector 150 and adjusting the main variable attenuator 134 and the mainphase shifter 136 in accordance with the output of the CCL powerdetector 150. As with other power detectors in the feedforward poweramplifier circuit, the output of an input power detector 116 is directedto a microprocessor (not shown), which may be contained in the monitorand control board 208, shown in FIG. 9. The voltage from the CCL powerdetector 150 is used to adjust the main variable attenuator 134 and themain phase shifter 136 to obtain maximum carrier cancellation out of theCCL 106. The microprocessor may or may not utilize the signal from theinput power detector 116 when determining adjustments for maximalcarrier cancellation.

The input power detector 116 may be provided on the main signal path 102to monitor the input power levels. For example, if the power level of acarrier signal is above or below a desired threshold, the voltage outputof the input power detector 116 may be used to trigger an errorcondition, such as a reset or power down.

After the RF carrier signals have been attenuated and phase shifted onpath 102, they are amplified by the main amplifier 138. The mainamplifier 138 produces or outputs, in addition to the desired amplifiedRF carrier signals, unwanted IMD products. The IMD products or error arecaused by inherent non-linearities within the main amplifier 138. If theRF carriers, for example, lie in several frequency bands, or designatedchannels, the IMD products from one frequency band may spill over intoother adjacent or nearby frequency bands or channels. This effectbecomes more pronounced the closer the main amplifier 138 is driven tosaturation.

Next, the amplified RF carrier signals and IMD products from the outputof amplifier 138 are time delayed by the main delay filter 140 toproduce delayed amplified RF carrier signals and delayed amplified IMDproducts on the main signal path 102. The time delay is chosen such thatthe amplified RF carrier signals and associated IMD products appear onthe main signal path 102 at substantially the same time that theadjusted carrier signals and IMD products from an error amplifier 124are coupled onto the main signal path 102. Since any delay introduced inthe signals input and output from the error amplifier circuit andassociated with the error signals requires corresponding delays andpower loss from the delay filter 140, the present invention, asdiscussed further below, minimizes delays in the input and outputbetween the error amplifier subcircuit and the delay line.

Meanwhile, on the feedforward path 104, a feedforward delay filter 118delays the RF carrier signals such that the RF carrier signals appear onthe feedforward path 104 at substantially the same time the attenuatedsample of the amplified RF carrier signals (and associated IMD products)are coupled onto the feedforward path 104 by a feedforward CCL coupler130. The carrier cancellation loop (CCL) 106 couples the amplified RFcarrier signals and associated IMD products on the main signal path 102onto the feedforward path 104 at the output of the feedforward delayfilter 118.

The CCL 106 includes (1) a main CCL coupler 126 which couples theamplified RF carrier signals and associated IMD products from the mainsignal path 102 onto the CCL 106, (2) a CCL attenuator 128 forattenuating the amplitude of the coupled signals, and (3) a feedforwardCCL coupler 130 which couples the amplified (and subsequentlyattenuated) RF carrier signals and associated IMD products onto thefeedforward path 104 at the output of the feedforward delay filter 118.The phase of the amplified RF carrier signals in the CCL 106 should beinverted (out of phase) with respect to the phase of the delayed RFcarrier signals on the feedforward path 104 after the feedforward delayfilter 118.

The CCL attenuator 128 attenuates the coupled signals such that theamplitude of the amplified RF carrier signals is substantially equal tothe amplitude of the delayed RF carrier signals on the feedforward path104, in order to obtain maximum carrier cancellation. Attenuationresulting from the main CCL coupler 126 and the feedforward CCL coupler130, as well as the gain of the main amplifier 138, in addition to thecoupling factor of the input carrier coupler 114, and the insertion lossof the feedforward delay filter 118 are taken into consideration whenselecting the attenuation factor for the CCL attenuator 128. The CCLattenuator 128 produces attenuated RF carrier signals and attenuated IMDproducts.

After coupling by the feedforward CCL coupler 130, the two out-of-phasecarrier signals cancel each other so that primarily the isolated IMDproducts are fed into the error amplifier subcircuit 16, thoughinsignificant levels of carrier products may also be present. In theerror amplifier subcircuit 16, these isolated IMD products are amplifiedand phase inverted (with respect to the amplified IMD products at theoutput of the main amplifier 138), so that the two signals will canceleach other when combined at the main ECL coupler 132.

The isolated IMD products are presented to the feedforward attenuator120, the feedforward phase shifter 122, and the error amplifier 124. Theamplitude of the isolated IMD products may be attenuated by thefeedforward attenuator 120, and the phase of the isolated IMD productsmay be shifted by the feedforward phase shifter 122, though notnecessarily in that order. The feedforward attenuator 120 andfeedforward phase shifter 122 are under the control of a suitablemonitor and control board 208 as shown in FIG. 9. Signal and power linesare passed through EMI filters to the monitor and control board 208.Examples of the signal lines include detector output, variableattenuator and phase shifter control lines, and bias monitor and controllines. The monitor and control board 208 is one type of printed circuitboard which can be used with one embodiment of the present invention inthe position shown in FIG. 9.

The attenuated and phase-shifted IMD products are amplified by erroramplifier 124. The gain of the error amplifier 124 is selected such thatthe IMD products cancel at the main ECL coupler 132, resulting insubstantial reduction of IMD products at the output 112. The erroramplifier 124 is operated well below saturation to avoid creatingnon-linear distortion products of its own in the error correction loop108.

The error amplifier 124 produces amplified IMD products whose phase isinverted with respect to the phase of the delayed amplified IMD productson the main signal path 102. The amplitudes of the amplified IMDproducts and the delayed amplified IMD products are substantiallyidentical. Because they are also phase inverted, when the amplifiedproducts are coupled by a main ECL coupler 132 onto the main signal path102, the amplified IMD products and the delayed amplified IMD productssubstantially cancel each other so that IMD products are essentiallyeliminated from the main signal supplied to the output 112.

The resultant amplified RF carrier signals are coupled onto a scanningreceiver 144 by a scanning receiver coupler 142. Optionally, a splitter146 may provide the amplified RF carrier signals to both the scanningreceiver 144 and to an output power detector 148. The scanning receiver144 produces an output voltage corresponding to the signal level in thechannel of interest. This signal is routed to an A/D converter for useby the microprocessor on the monitor and control board 208 (shown inFIG. 9). The output power detector 148 converts the amplified RF carriersignals to a voltage representative of their power. In one aspect of thepresent invention, the output power detector 148 monitors the outputpower of the main amplifier 138 for abnormalities, such as triggering afault alarm when, for example, too much power is detected. One suitablescanning receiver is discussed in copending U.S. Patent Applicationentitled “A Scanning Receiver for Use in a Feed-Forward Multi-CarrierPower Amplifier,” and filed on Mar. 6, 2001, which is incorporatedherein by reference in its entirety.

The feedforward power amplifier circuit 10 may include a circulator 152with an associated circulator attenuator 154. The circulator 152 servesto prevent the flow of reflected RF power from the output 112. An outputline from the circulator 152 is connected to a reverse output powerdetector 156, and signal from the reverse output power detector 156 isfed, for example, into a monitor and control board 208 for detection. RFpower entering the circulator 152 subsequently leaves the circulatoralong the next pathway crossed by the clockwise arrow. Thus, reflectedRF power from the output 112 exits toward the reverse output powerdetector 156 rather than toward the other circuit components, whichmight be damaged by reflected power.

As discussed above, the feedforward power amplifier circuit 10 isdivided into several subcircuits to be electrically isolated from oneanother. In accordance with one aspect of the invention, the amplifierchassis design provides a unique isolation scheme in a compact,non-complex, and low cost (manufacturing and material) package.Subcircuits may be grouped into component groups, or smaller subcircuitswithin the larger subcircuits of the present invention. In accordancewith an aspect of the invention, the main amplifier subcircuit and theerror amplifier subcircuit are positioned on a single circuit board. Inone embodiment of the present invention, the delay line filtersubcircuit 12 includes the following components: the input carriercoupler 114, the feedforward delay filter 118, the feedforward CCLcoupler 130, associated terminations 115, the CCL attenuator 128, themain CCL coupler 126, the main delay filter 140, the main ECL coupler132, the scanning receiver coupler 142, the circulator 152, and thecirculator attenuator 154.

As discussed further hereinbelow, various different delay linesubcircuits and associated component layouts and filter designs might beutilized in practicing the invention. For example, suitable delay linesubcircuits and filter designs are available from companies such asAndrew Corporation of Orland Park, Ill., Filtronic Comtek Ltd. of WestYorkshire, U.K. or Remec, Inc. of San Diego, Calif. The presentinvention, in accordance with various of its aspects, also utilizes auniquely positioned and interfaced error amplifier and delay linesubcircuit wherein the delay line subcircuit, regardless of its specificdesign, is machined or cast into a chassis of the amplifier. The erroramplifier is positioned generally directly thereabove and is coupledgenerally directly to the delay line subcircuit with minimal delayintroduced at the interface between the two circuits. Further detailsare set forth below.

In the design disclosed herein, the main amplifier subcircuit 14includes the following components or subcircuits: the input powerdetector 116, the main variable attenuator 134, the main phase shifter136, and the main amplifier 138.

The error amplifier subcircuit 16 includes the optional CCL powerdetector 150, the feedforward attenuator 120, the feedforward phaseshifter 122, and the error amplifier 124.

The forward power detector subcircuit 18 includes the output powerdetector 148.

The scanning receiver subcircuit 20 includes the optional splitter 146,the scanning receiver 144, and a scanning receiver power detector 145.

Finally, the reverse power detector subcircuit 22 includes the reverseoutput power detector 156.

The subcircuits are connected via appropriate connectors as shown inFIG. 1 by connector arrows, “-->>--”. In accordance with one aspect ofthe invention, connections between the error amplifier subcircuit 16 andthe delay line subcircuit 12 is accomplished by a direct coax connectorwhich is soldered or otherwise coupled at one end to the circuit boardwith the error amplifier thereon, and is press-fit through a hole in thechassis to make a direct connection to the delay line subcircuit. Thevarious subcircuits may be connected via direct connections utilizingblind-mate coaxial connectors, or the connections may be made usingconnectorized coaxial cables. The dotted lines, “A” of FIG. 1, are usedto demarcate subcircuit boundaries where RF-isolating walls, accordingto another aspect of the present invention, are preferably located. Itis to be understood that the features of the present invention may becustomized to fit a variety of alternative amplifier designs andconstructions. For example, though a single loop feedforward poweramplifier is discussed in connection with the present invention, theprinciples of the present invention may also be applied to double loopfeedforward power amplifiers or any other type of amplifier utilizingone or more delay lines to improve linearity.

Turning now to FIGS. 2-11, perspective and cutaway views of portions ofa feedforward power amplifier embodiment according to the principles ofthe present invention are shown. The present invention uses a uniquecombination of a chassis body and lid structure design for achievingvarious aspects of the invention, such as reduced complexity, simplerand more cost effective construction, and desirable isolation andefficiency.

The chassis 202 of the present invention may be manufactured of avariety of materials and in a variety of sizes. In one embodiment,aluminum is used for the complete chassis and aluminum is particularlypreferred for its ability to conduct heat in the main chassis body 206.Aluminum alloys may also be used. In one embodiment, zinc is used forshielding in the inner lid 204. Though the chassis, according to oneembodiment of the present invention, is cast out of aluminum or aluminumalloys, it is to be understood that the chassis and components,according to the present invention, may be formed by other methods,including machining of metals, casting of metallized plastic, andcasting plastic with surface metallization applied later.

Referring to FIG. 9, chassis 202 comprises a lid structure or liddesignated as an inner lid 204 and a main chassis body 206 covered by anouter lid 314 to close the chassis. The term “lid” is used herein todesignate a structure which covers a portion of the subcircuits forisolation, and such term is not meant to be limiting with respect to howthe structure interfaces with chassis body 206. The main chassis body206 includes a delay line subcircuit portion 290 formed therein (seeFIGS. 10 and 11) for housing the delay line subcircuit 12. The bottomside 220 of the inner lid 204 is configured to include, among othercavities, a main amplifier cavity 214 which houses and isolates the mainamplifier subcircuit 14 and an error amplifier cavity 216 which housesand isolates the error amplifier subcircuit 16. These cavities andsubcircuits are visible in FIG. 9, which shows a cross-sectional sideview of the chassis 202.

In accordance with one aspect of the present invention, the unique innerlid 204 is configured to isolate various subcircuits, both above andbelow the main plane of the inner lid. In one embodiment of theinvention, those various subcircuits might be on individual boards whichare thereby individually isolated. For example, one embodiment describedherein utilizes separate main amplifier and error amplifier boards.However, in one particularly desirable embodiment, and in accordancewith one aspect of the present invention, both the main amplifiersubcircuit and error amplifier subcircuit and related components areconfigured on a single circuit board. Such a configuration is desirablefor reducing the complexity of the overall amplifier design and therebyreducing material and production costs. Utilization of the mainamplifier subcircuit and error amplifier subcircuit on a single circuitboard is possible due to the unique configuration of the chassis 202 ofthe present invention, and particularly the unique configuration of theinner lid 204, which affords high levels of isolation between the mainamplifier and the error amplifier.

Accordingly, herein, both individual board embodiments and a singleboard embodiment are disclosed. For example, FIG. 3 illustrates a bottomview of the inner lid 204 utilized with individual main amplifier anderror amplifier boards. However, the embodiment as illustrated in FIGS.3A and 3B, illustrate, respectively, a bottom view of an inner lidembodiment 204 a, and an embodiment of a single circuit boardincorporating both a main amplifier subcircuit and an error amplifiersubcircuit, to be used with lid 204 a.

The different embodiments 204, 204 a of the inner lid are generallysimilar at a top side 226, and also have some similarities along thebottom side 220. Therefore, in describing the different embodiments ofthe invention herein similar reference numerals will generally beutilized to set forth any similar features between the embodiments 204,204 a of the inner lid.

A printed circuit board, such as a monitor and control board 208, whichfunctions to monitor and control the operation of the feedforward poweramplifier circuit 10, is mounted above a top side 226 of the inner lid204, 204 a. The top side 226 of the inner lid 204, 204 a includes upperinterstage cavities which, in accordance with one aspect of theinvention, provide electromagnetic isolation for RF subcircuits mountedon the bottom side of the monitor and control board 208. The upperinterstage cavities are formed by upper interstage walls 227 (as seen inFIGS. 2 and 9) which are configured in the inner lid to extend upwardlyfrom the top side or surface 226 of the inner lid 204, 204 a.

The inner lid 204, 204 a has a generally horizontally disposed floorstructure 205 which defines the top side 226 and the bottom side 220 ofthe inner lid. That floor structure generally defines a plane from whichthe upper interstage walls 227 extend upwardly and lower interstagewalls 280 extend downwardly for defining the various interstage cavitiesin accordance with the principles of the present invention. That is,interstage walls extend generally in opposite directions from the planedefined by floor structure 205 to produce the isolation betweensubcircuits, which are positioned both above the inner lid 204, 204 a,and below the inner lid. The designation of certain sides or walls asupper/lower or top/bottom is not limiting with respect to how theamplifier might ultimately be oriented.

In one embodiment of the invention, such walls are machined or castdirectly into the inner lid for reducing the complexity of the shieldingand reducing the overall manufacturing costs. Alternatively, theinterstage walls might be otherwise coupled or fastened to the innerlid.

As illustrated in FIGS. 2, 3, and 3A, the inner lid also includes sidewalls 224 which extend around the periphery of the inner lid and extendupwardly and downwardly with respect to the floor structure 205.

The interstage cavities on side 226, as shown in FIG. 2, include aforward power detector cavity 228 and a reverse power detector cavity230 adapted, respectively, to isolate the forward output power detectorsubcircuit 18 and the reverse power detector subcircuit 22. Otherinterstage cavities on the top side 226 of the inner lid 204, 204 a areadapted to hold components of the scanning receiver subcircuit 20. Theseinclude a power divider cavity 232, a downconverter cavity 234, a localoscillator cavity 236, a first intermediate frequency (IF) stage cavity238, a second IF stage cavity 240, a third IF stage cavity 242, and adetector stage cavity 244. The purposes of the IF stages are twofold.The first purpose is to amplify a downconverted signal such that adetector is provided with appropriate signals for proper detectoroperation. The second purpose of the IF stages is to provide filteringso that the detector reacts solely to the desired signal.

Also shown in FIG. 2 are several through holes 246, 248, and 250, whichallow signal connections, including filtered signal connections, betweencircuits positioned above and below the through holes on either side ofthe lid 204, 204 a. In one embodiment, a first through hole 246 is amain amplifier/monitor and control board connection through hole adaptedto allow a filtered signal connection between the monitor and controlboard 208 positioned above the inner lid 204, 204 a and the mainamplifier subcircuit 14, and a second through hole 248 is an erroramplifier/monitor and control board connection through hole adapted toallow a filtered signal connection between the monitor and control board208 positioned above the inner lid 204, 204 a and the error amplifiersubcircuit 16 positioned below the inner lid 204.

Turning now to the bottom sides of lid 204, 204 a, FIGS. 3, 3Aillustrate different embodiments of the invention for use with multipleamplifier circuit boards and a single amplifier circuit board,respectively. Referring first to FIG. 3A, that figure illustrates a lid204 a for use with a single amplifier board that contains both the mainamplifier and the error amplifier. The bottom side 220 of inner lid 204,204 a, according to one embodiment of the present invention, has twodefined large cavities, a main amplifier cavity 214 and an erroramplifier cavity 216, which are isolated using a dividing wall 218 a.The dividing wall 218 a provides electromagnetic isolation between themain amplifier subcircuit 14 and the error amplifier subcircuit 16. Thewall 218 a protrudes from the bottom side 220 of the inner lid 204.While providing the desired isolation between the error amplifier andthe main amplifier, wall 218 a allows for the positioning of the mainamplifier subcircuit and the error amplifier subcircuit on the samecircuit board. The board spans across wall 218 a, and because of theunique configuration of the wall 218 a, the desired electromagneticisolation is maintained.

Specifically, referring to FIG. 3B, a circuit board 219 is shown whichincludes generally a main amplifier section 221, and an error amplifiersection 223. When the board is positioned below the inner lid, asillustrated in FIG. 9, various of the cavities defined by the walls 280of the inner lid 204 a separate various of the subcircuits of both themain amplifier and the error amplifier. Furthermore, the dividing wall218 a provides the desired isolation between the main and erroramplifiers.

Referring to FIG. 3A, wall 218 a includes a series of end-to-end islandportions or islands 225 with open areas 227 therebetween positionedalong at least a portion of the wall's length. On the other hand, thesingle circuit board 219 has a series of cut-outs 229 which are milledinto the circuit board 219. The various cut-outs 229 define spanningportions 231 which span between the main amplifier section 221 and theerror amplifier section 223 of the board 219 to define a single circuitboard in accordance with one aspect of the present invention. Referringto FIGS. 3A and 3B, the cut-outs 229 are positioned to correspond to thevarious islands 225 in the bottom side of lid 204 a, such that when thelid 204 a and board 219 are coupled together, a portion of the dividingwall 218 a, in the form of the islands 225, extends through the boardand contacts the chassis periodically along the length of the wall 218a, through the cut-outs. In that way, isolation can be maintained eventhough a single circuit board is utilized. This significantly reducesthe complexity of production by having both the main and erroramplifiers on a single board. The dividing wall 218 a is thereby incontact with the chassis body floor 222 where the inner lid 204 a andchassis body 206 are joined. Likewise, side walls 224 of lid 204 a arein conductive contact with the chassis body floor.

As noted, the main amplifier and error amplifier cavities are separatedby dividing wall 218 a which electrically contacts the main chassis bodyfloor 222 as shown in FIG. 9, at least along sections of its length. Inthis embodiment, the main amplifier cavity 214 and the error amplifiercavity 216 both contain various subcavities designed to enclose andisolate subcircuits of the main amplifier subcircuit 14 and the erroramplifier subcircuit 16 through the walls 280. In the main amplifiercavity 214, the subcavities include a main amplifier input subcavity252, a main amplifier input detector subcavity 254, a main amplifierphase shifter and variable attenuator subcavity 256, a main amplifierdriver stage subcavity 258, a main amplifier final driver stagesubcavity 260, and a DC power input subcavity 262, and a main amplifierfinal stage subcavity 264. In the error amplifier cavity 216, thesubcavities include an error amplifier input subcavity 268, an erroramplifier phase shifter and variable attenuator subcavity 270, an erroramplifier carrier correction loop detector subcavity 272, an erroramplifier driver stage subcavity 274, an error amplifier final driverstage subcavity 276, and an error amplifier final amplifier stagesubcavity 278. The subcavities are separated by various lower interstagewalls 280, which depend downwardly from floor 205 and which serve toisolate components within the subcavities from radio frequencyinterference from adjacent subcavities and also to add structuralrigidity to the inner lid 204. Lower interstage wall gaps 282 areincluded in lower interstage walls 280 so that components may beconnected to other components in different subcavities. The inneramplifier dividing wall 218, 218 a is provided with fastener holes 284which allow fasteners such as screws to pass through so that the innerlid 204 is securely fastened to the main chassis body 206. Otherfastener holes 284 are located throughout the inner lid 204, to allowthe monitor and control board 208 to be securely fastened to the innerlid 204 and to further provide for a more secure assembly when the innerlid 204 is secured to the main chassis body 206. Other embodiments maynot use screw fasteners, but might use other means to fasten, such asrivets or solder along the perimeters.

FIG. 3 illustrates an inner lid 204 for an alternative embodiment of theinvention which utilizes separate main amplifier and error amplifierboards. That is, each of the main amplifier and error amplifier andtheir respective components are located on individual circuit boards. Asmay be seen in FIG. 3, amplifier dividing wall 218 extends generallycontinuously across the inner lid to provide generally completeseparation between the main amplifier subcircuit and the error amplifiersubcircuit and their respective circuit boards. Therefore, FIG. 3discloses a multiple board embodiment, rather than a single boardembodiment as discussed with respect to FIGS. 3A and 3B. Other similarcomponents, features and subcavities are set forth in FIG. 3 withreference numerals similar to those utilized in FIG. 3A.

When the inner lid 204 is positioned and coupled to the chassis body206, the inner lid contacts the chassis body generally along the lengthof the dividing wall 218 for isolation between the main amplifier anderror amplifier, as opposed to the discrete contact points provided bythe islands 225 of wall 218 a.

Referring to FIGS. 3B and 9, gaskets 280 a, such as EMI gaskets, arecoupled to the circuit board 219 wherever the walls 280, or 218 a,contact the board 219. FIG. 3B illustrates the embodiment of theinvention utilizing a single board for both the main amplifier and erroramplifier. However, similar gaskets are utilized for the multiple boardembodiment as well. The EMI gasket material is soldered or otherwisesecured to the board at the various boundaries defined by the subcircuitcomponents and the subcavities formed by the bottom of the inner lid204, 204 a. Referring to FIG. 3B, gasket material 280 a, or rather,pieces of material, extend end-to-end along where the dividing wall 218a would engage the chassis. Such gasketing is to address those areasbetween the islands 225 where the board makes contact with the wall openareas 227 between the islands 225. However, in a version utilizingseparate boards, generally gasketing material along the dividing wall218 would not be necessary, as the wall would contact the chassisgenerally along its length. The gasketing material 280 is a compressibleElectro Magnetic Interference (EMI) material used to fill gaps remainingbetween the lower interstage walls 280 and the respective circuit boardsor board. In one embodiment, the gasketing may be that manufactured bythe W. L. Gore Company, (Goreshield SMT-EMI Gasketing, Gore Part No.3645-10).

In this embodiment, a strip of gasketing is attached to a strip ofmetal, and the metal is soldered onto a circuit board along with thecircuit components. This type of gasketing is preferred for its abilityto complete an RF and EMI isolating Faraday cage when circuit board andchassis tolerances are such that full intimate metal-to-metal andmetal-to-board contact cannot be guaranteed over the entire desiredmating area. Another embodiment involves application of a dispensed beadof gasketing along inner lid side walls 224 and/or along lowerinterstage walls 280. One type of dispensed gasketing that may be usedin this embodiment is Chomerics, Cho-Form Form-In-Place EMI gasketing.

Turning now to FIG. 4, a perspective view of the main chassis body 206shows the main chassis body floor 222 having several through holesallowing for connections through the main chassis body floor 222 andthrough the side walls 286 of the main chassis body 206. The mainchassis body 206 also has depressions 288 provided in the main chassisbody floor 222 to accommodate through-hole components, board bottom-sidetraces, and chassis mounted components. In one embodiment, through holesthrough the main chassis body floor 222 are provided to allowconnections between a delay line subcircuit portion 290 and the mainamplifier subcircuit 14 and error amplifier subcircuit 16. Through holesvisible in FIG. 4 include a main connector through hole 292 to accept amain connector including connectors for the input 100 and output 112, amain amplifier output through hole 294 adapted to allow connectionbetween the main amplifier subcircuit 14 and the delay line subcircuitportion 290, and an error amplifier input through hole 296 adapted toallow connection between the error amplifier subcircuit 16 and the delayline subcircuit portion 290.

FIG. 5 shows a top view of the main chassis body 206 and floor 222,including through holes and fastener holes. Through holes visible inFIG. 5 include a main amplifier input through hole 298 adapted to allowconnection between the delay line subcircuit portion 290 and the mainamplifier subcircuit 14, an input through hole 300 adapted to allowconnection between the input 100 and the delay line subcircuit portion290, and an output through hole 302 adapted to allow connection betweenthe output 112 and the delay line subcircuit portion 290. Also shown inFIG. 5 are a forward power detector through hole 304 adapted to allowconnection between a forward power detector subcircuit 18 and the delayline subcircuit portion 290, a reverse power detector through hole 306adapted to allow connection between a reverse power detector subcircuit22 and the delay line subcircuit portion 290, and an error amplifieroutput through hole 308 adapted to allow connection between the erroramplifier subcircuit 16 and the delay line subcircuit portion 290.Fastener holes shown in FIG. 5 include main chassis body floor fastenerholes 310 adapted to allow fastening of main amplifier subcircuit 14 anderror amplifier subcircuit 16 components to the main chassis body floor222 and outer lid fastener holes 312 adapted to allow fastening of anouter lid 314 (visible in FIG. 9) to the main chassis body 206 and innerlid fastener holes 313 for fastening the inner lid to the chassis 206.

FIG. 6 shows the main chassis body 206 housing the main amplifiersubcircuit 14 and the error amplifier subcircuit 16. The main and erroramplifier subcircuits may be on separate boards or may be on a singleboard, as illustrated in FIG. 3B. FIG. 3B uses similar referencenumerals to FIG. 6 to show the location of the various subcircuits. Anamplifier power supply 316 is housed within an amplifier power supplycavity 318. Cooling fins 320, integral to the main chassis body 206,serve to dissipate heat generated by the amplifier power supply 316, themain amplifier subcircuit 14, and the error amplifier subcircuit 16. Thedelay line subcircuit portion 290 of the main chassis body 206 is shownin a position beneath the error amplifier subcircuit 16 in accordancewith one aspect of the invention. The present invention eliminatessignificant delays between the input and output from the error amplifierto the delay line circuit by locating the delay line circuit below theerror amplifier, machining or configuring the delay line subcircuit anddelay filters directly into the chassis, and providing directconnections between the error amplifier and the delay line subcircuit.

FIG. 6 shows the components and subcircuits of the main amplifiersubcircuit 14 which are isolated by the dividing wall 218, 218 a andlower interstage walls 280 of the inner lid 204. The subcircuits andcomponents are numbered in agreement with the numbering of theircorresponding cavities shown in FIGS. 3 and 3A. These subcircuits andcomponents include a main amplifier input subcircuit 252 a, a mainamplifier input detector subcircuit 254 a, a main amplifier phaseshifter and variable attenuator subcircuit 256 a, a main amplifierdriver stage 258 a, a main amplifier final driver stage 260 a, a mainamplifier DC power input 262 a, and a main amplifier final amplifierstage 264 a. A portion of the main amplifier final amplifier stage 264 aextends above the delay line subcircuit portion 290, to provide for ashort connection between the main amplifier subcircuit 14 and the delayline subcircuit portion 290.

FIG. 6 further shows the components and subcircuits of the erroramplifier subcircuit 16 which are isolated by the dividing wall 218, 218a and the lower interstage walls 280 of the inner lid 204. Thesesubcircuits and components include an error amplifier input subcircuit268 a, an error amplifier phase shifter and variable attenuatorsubcircuit 270 a, an error amplifier carrier correction loop detector272 a, an error amplifier driver stage 274 a, an error amplifier finaldriver stage 276 a, and an error amplifier final amplifier stage 278 a.As noted above, the error amplifier subcircuit 16 is positionedgenerally directly above the delay line subcircuit portion 290 inaccordance with one feature of the invention to provide for directcoaxial connector connections between the error amplifier subcircuit 16and the delay line subcircuit portion 290 in accordance with anotherfeature of the invention. The various combination of features, includingthe error amp positioned above the delay line circuit which is machinedand/or formed in the chassis, and particularly including the directinterconnect, using no coaxial cables, provides several key benefits forthe present design. For example, a shorter overall delay is required ofthe main delay filter 140. This provides a desirable smaller physicalsize and a lower insertion loss for the main delay filter 140.Furthermore, the invention features result in less loss and a higheramplifier power efficiency which is a significant benefit of thisinventive amplifier design and packaging technique.

FIGS. 10 and 11 show side and bottom views, respectively, of the chassisincluding the delay line cavity and the direct coaxial interconnectionbetween the error amplifier and the delay line subcircuit.

The main chassis body 206 houses the delay line subcircuit 12 within thedelay line subcircuit portion 290, which, as shown in FIGS. 9 and 10, islocated below the main chassis body floor 222, next to the fins 320. Inthe embodiment of the circuit shown in FIG. 1, eight connectors,demarcated in FIG. 1 by the connection arrows (“-->>--”) and circles,are provided between the delay line filter subcircuit 12 and othersubcircuits of the feedforward power amplifier circuit 10. The circlesare assigned reference numerals corresponding to the connection holesshown in FIG. 5. In one embodiment, these connections may be provided byeight press-fit blind-mate RF coaxial connectors which protrude throughthe main chassis body floor 222 to allow RF interconnections between thedelay line filter subcircuit 12 and other subcircuits.

Referring to FIG. 10, a side view of the chassis main body 206 and outerlid 314 is shown similar to that shown in FIG. 9, except without theinner lid and main amplifier board illustrated. A delay line lid 291 isshown covering a delay line cavity 325 formed in the chassis forcontaining and supporting the delay line subcircuit components. Onesuitable delay line subcircuit portion 290 of the chassis is illustratedin FIG. 11 and is discussed further hereinbelow. Turning again to FIG.10, one suitable direct-connection coaxial connector 330 is illustrated.Connector 330 includes a coaxial plug 332 positioned at an end of theconnector proximate to the error amplifier subcircuit 16, andparticularly proximate to the circuit board which contains the erroramplifier subcircuit. As noted above, that circuit board may either bean individual board, or may be a portion of a larger, single board whichholds both the main amplifier subcircuit and the error amplifiersubcircuit. In any case, the coaxial plug 332 is appropriatelyelectrically connected to a suitable connection point of the erroramplifier board, such as by being soldered to the error amplifier board.The coaxial jack portion 334 of the connector is then press fit into anappropriate chassis through hole, such as through hole 308 or 296, asillustrated in FIG. 5. A nipple portion 336 at the end of the coaxialjack portion 334 provides for connection to a suitable point within thedelay line subcircuit portion 290, according to procedures known to aperson of ordinary skill in the art. The unique positioning of the erroramplifier board and error amplifier subcircuit 16 and components abovethe delay line subcircuit portion 290 and circuit 12 provided by theinvention, in combination with the delay line subcircuit portion beingintegrally formed and positioned within the chassis body 206, allows thedirect press-fit coaxial connection between the error amplifier 16 andthe delay line subcircuit 12, thus eliminating cable interconnects whichintroduce delays and which must then be addressed by the delay linefilter 140 and the subcircuit. Such additional delays cause additionalpower losses within the delay line subcircuit, and thereby reduce theefficiency of the overall amplifier. The present invention enhancesefficiency by providing direct interconnection between the erroramplifier and the delay line subcircuit to reduce such delays and powerlosses. In a preferred embodiment, both the input and outputinterconnects 330 and 332 for the error amplifier utilize directinterconnects, as illustrated in FIG. 10. A single interconnect 330 isillustrated in FIG. 10, but it will be readily understood that multiplesuch interconnects can be utilized.

The delay line subcircuit portion 290 is formed in the chassis body 206and includes delay line subcircuit metalwork adapted to guide and delayRF signals, in accordance with principles known to those skilled in theart. In accordance with one aspect of the invention, the metal workportions, which generally represent the delay filters 118, 140 of thedelay line subcircuit 12, are fabricated into chassis body 206, andgenerally into cavity 325 (see FIG. 10). The delay line subcircuitportion may be provided with a removable lower lid 291 to allow forassembly. The delay line subcircuit portion 290 and cavity 325 also willgenerally contain circuit boards, including drop-in coupling andtransition circuitry provided within the delay line subcircuit 12. Forexample, as illustrated in one embodiment, the delay line subcircuitutilizes two delay lines or filters 118, 140, five couplers (114, 130,126, 132, 142), and a circulator 152. These circuits may comprisefurther subcircuits within the delay line subcircuit portion 290.Coupling paths for the circuits may be provided in the delay linesubcircuit portion. The delay line subcircuit portion metalwork, in oneembodiment, includes cylindrical cavities which act as resonatingfilters to accomplish signal delays. Such resonating cavity delaystructures are known to persons of ordinary skill in the art and designsfor such structures, along with supporting circuitry, are commerciallyprovided by companies such as Andrew, Filtronic Comtek and Remec, asmentioned above. The provision of a delay line subcircuit portion 290integral with the feedforward power amplifier chassis 202 and positionedbelow the error amplifier, imparts a number of benefits to the design,construction, and use of the feedforward power amplifier 10, asdiscussed

The positioning of the error amplifier subcircuit in an error amplifiersubcircuit cavity 216 directly above the delay line filter subcircuit 12in cavity 325 and the use of direct connect coax connectors minimizesthe required length of an output delay line and the size of filter 140to a significant extent, since no significant extra delay is added tothe error amplifier subcircuit from lossy interconnect cables. Theresulting direct delay line connection results in a lower delay lineloss, which proportionally increases overall efficiency of thefeedforward power amplifier 10 of the invention.

More specifically, the use of an integrated delay line filter subcircuit12, according to the present invention, and the direct interconnect,results in shorter delay in the main delay filter 140, less signal loss,smaller size, and higher efficiency of the feedforward power amplifier10. In one embodiment, the delay line subcircuit portion 290 includestwo delay filters and lines, but other embodiments may house one or morethan two delay lines for providing required signal delays. A first delayfilter or line included in the delay line subcircuit portion 290 of thedisclosed embodiment is the main delay filter 140 and a second delayfilter or line included in the delay line subcircuit portion is thefeedforward delay filter 118. In some embodiments, delays provided bythe delay line subcircuit portion 290 may range from about 7 ns to about15 ns, though longer or shorter delays may be provided based onamplifier design considerations. In one embodiment, the delay providedby the main delay filter 140 is around 7.25 ns and the delay provided bythe feedforward delay filter 118 is around 11 ns.

Referring to FIG. 11, a bottom view of the chassis body 206 is shown inpartial cross-section, illustrating schematically the delay linesubcircuit 290 which includes delay lines or filters 140, 118 along withvarious of the other components, such as couplers and circulatorsassociated with the delay line subcircuit. The various circuits andcomponents other than the resonator cavities of the delay lines 118 and140, are positioned on appropriate circuit boards with appropriateconnectors as dictated by the specific design of the delay linesubcircuit. It will be understood that other, different components mightbe utilized in a different arrangement from that shown in the embodimentillustrated in FIG. 11. Reference numerals are set forth on FIG. 11 tocorrespond to the various connection points and components of the designillustrated in FIG. 1. An input signal 100 is directed to both the mainamplifier at through hole 298, and through a coupler 114 to thefeedforward path. In the feedforward path, the signal is directedthrough the delay filter 118 in the form of the resonating cavitiesmachined and constructed into the chassis body 206 in accordance withone aspect of the invention. Various other components of the delay linesubcircuit 290 are illustrated along the signal paths through theamplifier. Delay filter 140 is also in the form of resonating cavities.The various through holes and connection points into and out of thedelay line subcircuit are illustrated with reference numeralscorresponding to those in FIG. 1 and FIG. 5.

Turning now to FIG. 8, a top cutaway view of the feedforward poweramplifier 10 shows connections between components of the feedforwardpower amplifier 10. Connections between components of the feedforwardpower amplifier may be provided by the direct interconnects noted above,or cabled interconnects. Direct interconnects are preferably used forkey connections where delay or insertion loss from a cabled interconnectwould adversely affect the performance of the feedforward poweramplifier circuit 10, and they consist of blind-mate RF coaxialconnectors integrally connected to each other. As shown in FIG. 8 and asdiscussed above, direct interconnects with the delay line filtersubcircuit 12 in the delay line subcircuit portion 290 include an erroramplifier input interconnect 330 and an error amplifier outputinterconnect 332. Other interconnects may be cabled between the delayline filter subcircuit 12 and circuit boards containing othersubcircuits. Cabled interconnects have two coaxial terminationsconnected by a coaxial cable. In one embodiment, as shown in FIG. 8,these interconnects include a main amplifier output interconnect 328, aforward power interconnect 334, a reverse power interconnect 336, anoutput interconnect 338, an input interconnect 340, and a main amplifierinput interconnect 342.

Turning now to FIG. 7, the inner lid 204 is shown positioned within themain chassis body 206 to cover, contain, and isolate the subcircuits onthe board or boards. A main connector 322 is shown extending through themain connector through hole 292. The main connector 322 includesconnectors for all input and output signals delivered to and from thefeedforward power amplifier 10. A main amplifier/monitor and controlboard EMI filter-type connector 324 is shown extending through the mainamplifier monitor and control board connection through hole 246 and anerror amplifier/monitor and control board EMI filter-type connector 326is shown extending through the error amplifier/monitor and control boardconnection through hole 248. As shown in FIG. 9, the monitor and controlboard rests atop and is fastened to the inner lid 204 when thefeedforward power amplifier 10 is fully constructed.

In a completely constructed amplifier, the relationship between thesubcircuits of the feedforward power amplifier 10, and the chassis 202consisting of the main chassis body 206, and the inner lid 204 isfurther illustrated in FIG. 9, which shows a cross-sectional view of thefeedforward power amplifier 10 on one embodiment of the invention. Theinner lid side walls 224 and the inner lid amplifier dividing wall 218,218 a are in electrical contact with the main chassis body floor andform the main amplifier cavity 214 and the error amplifier cavity 216.In a single board version of the invention, with both the main amplifierand error amplifier on a single board, the wall 218 a is constructedwith islands 225 which protrude through the board cutouts 229, thusallowing the board to span across the wall. In the multiple boardembodiment, the wall 218 generally contacts the chassis floor along itslength. Lower interstage walls 280 are shown extending downward from thebottom side 220 of the inner lid 204. The compressible electromagneticinterference (EMI) shield gasketing material 280 a is used to fill gapsremaining between the lower interstage walls 280 and their respectivecircuit boards.

The interstage cavities along the top of the inner lid 204 are boundedby the inner lid 204, including the inner lid side walls 224 and theupper interstage walls 227, and the monitor and control board 208. Thepresent invention has an integral lid providing shielding both on anupper surface and a lower surface for different components of theamplifier. This forms a very compact, low-cost and simple design whichprovides the desired isolation and shielding between the varioussubcircuits. In addition to their shielding function, the upperinterstage walls 227 provide a surface for mounting the monitor andcontrol board 208. The subcavities along the bottom of the inner lid 204are bounded by the inner lid 204, including the inner lid side walls224, the lower interstage walls 280, and the inner amplifier dividingwall 218, the main amplifier subcircuit 14 and the error amplifiersubcircuit 16. Due to the compressible EMI shield gasketing 227 a and280 a, the side walls 224 of the inner lid 204, the lower interstagewalls 280, the inner lid amplifier dividing wall 218 and the lowersurface of the inner lid 204, all subcircuits and components of thefeedforward power amplifier 10 which might otherwise interfere with eachother's operation are shielded. In one embodiment, the lower interstagewalls 280 extend downwardly from the bottom side 220 of the inner lid204 to within approximately 20 mils of their respective circuit boardsurfaces to electromagnetically isolate components and subcircuits ofthe main amplifier subcircuit 14 and the error amplifier subcircuit 16.Though a particular conformation for the inner lid 204 and the mainchassis body 206 has been described, it is to be understood thatalternative arrangements of interstage cavities and subcavity walls maybe utilized for different circuit designs.

The chassis 202 of the present invention may be manufactured of avariety of materials and in a variety of sizes. In one embodiment,aluminum is used for the complete chassis and aluminum is particularlypreferred for its ability to conduct heat in the main chassis body 206.Aluminum alloys may also be used. In one embodiment, zinc is used forshielding in the inner lid 204. Though chassis, according to the presentinvention, are preferably cast out of aluminum or aluminum alloys, it isto be understood that chassis according to the present invention may beformed by other methods, including machining of metals, casting ofmetalized plastic, and casting plastic with surface metallizationapplied later.

The design of the present invention preferably achieves isolationbetween subcircuits greater than approximately 100 dB (decibels). Theisolation achieved according to the present invention is comparable tothat achieved through the use of a multiple separate chassis for eachsubcircuit which is a larger, more complex and more expensive design. Inone embodiment, the inner lid 204 is connected to the main chassis body206 via connection screws located along the inner amplifier dividingwall 218. Chassis wall, floor, lid, and side thicknesses of at leastapproximately 70 mils are used in the disclosed embodiment of thepresent invention, though thicknesses greater than or less than 70 milsmay be used, based on casting ability and weight and sizeconsiderations.

Electromagnetic isolation is achieved because a Faraday cage isconstructed around all cavities having components producingelectromagnetic interference. Further, the combination of normallyseparate chassis into a single chassis design reduces the cost ofchassis casting or machining. The cost of casting or machining aseparate delay line subcircuit portion is reduced to the cost ofmachining of the delay line subcircuit portion 290 into the main chassisbody 206. Further, the elimination of interconnect cables betweenseparate chassis, the elimination of individual shield assemblies, andthe reduction of fastening hardware result in lower cost because lessmaterial is used than in conventional amplifier construction.

While the present invention has been described with reference to one ormore particular embodiments, those skilled in the art will recognizethat many changes may be made thereto without departing from the spiritand scope of the present invention. Each of these alternativeembodiments and obvious variations thereof is contemplated as fallingwithin the spirit and scope of the claimed invention, which is set forthin the following claims.

1. An amplifier comprising: a main amplifier subcircuit and an erroramplifier subcircuit each directly mounted together on a single circuitboard; a chassis body; a lid structure for positioning with the chassisbody to contain the circuit board and main and error amplifiersubcircuits; one of the lid structure and the chassis body havinggenerally solid side walls extending therefrom for defining a mainamplifier cavity with subcavities to contain subcircuits of the mainamplifier subcircuit and an error amplifier cavity with subcavities tocontain subcircuits of the error amplifier subcircuit, the side wallsextending to contact the circuit board to isolate the subcircuits; theone of the lid structure and chassis body further including a generallysolid dividing wall, of greater thickness than the side walls, extendingbetween the main amplifier subcircuit and the error amplifiersubcircuit, the dividing wall having multiple broad islands extendingtherefrom, the multiple islands passing through multiple cut-outs formedin the circuit board between the main amplifier subcircuit andrespective cavity and the error amplifier subcircuit and respectivecavity to electrically couple to the other of the lid structure andchassis body to separate the amplifier cavities and electrically isolatethe main and error amplifier subcircuits.
 2. The amplifier of claim 1wherein the side walls are integrally formed with the lid structure. 3.The amplifier of claim 1 wherein the side walls extend from the lidstructure and further comprising additional subcircuits, the lidstructure including at least one other side wall extending from a sideof the lid structure opposite the side wall for isolating subcircuits onboth sides of the lid structure.
 4. The amplifier of claim 1 furthercomprising a gasket coupled between the side wall and a circuit boardfor isolating the subcircuit.
 5. A method of isolating subcircuits of anamplifier comprising: mounting each of a main amplifier subcircuit andan error amplifier subcircuit directly on a single circuit board in achassis body; positioning a lid structure with the chassis body tocontain the circuit board and amplifier subcircuits, at least one of thelid structure and the chassis body having generally solid side wallsextending therefrom for defining a main amplifier cavity withsubcavities to contain subcircuits of the main amplifier subcircuit andan error amplifier cavity with subcavities to contain subcircuits of theerror amplifier subcircuit; positioning the single circuit board so thatthe side walls extend to contact the circuit board to isolate thesubcircuits within the main amplifier cavity and the error amplifiercavity; positioning a generally solid dividing wall, depending from oneof the lid structure and the chassis body, between the main amplifiercavity and the error amplifier cavity, the dividing wall having agreater thickness than the side walls; passing multiple broad islands,extending from the dividing wall, through multiple cut-outs formed inthe circuit board between the main amplifier subcircuit and respectivecavity and the error amplifier subcircuit and respective cavity toelectrically couple to the other of the lid structure and chassis bodyto separate the amplifier cavities and electrically isolate the main anderror amplifier subcircuits.
 6. The method of claim 5 wherein the sidewalls are integrally formed with the lid structure.
 7. The method ofclaim 5 wherein the side walls extend from the lid structure and the lidstructure includes at least one other side wall extending from a side ofthe lid structure opposite the other side walls, and further comprisingpositioning additional subcircuits proximate the one other side forisolating subcircuits on both sides of the lid structure.
 8. The methodof claim 5 further comprising coupling a gasket between the side walland a circuit board for isolating the subcircuit.
 9. An amplifiercomprising: a main amplifier subcircuit and an error amplifiersubcircuit each directly mounted together on a single circuit board; achassis body; a lid structure for positioning with the chassis body tocontain the circuit board and main and error amplifier subcircuits; thelid structure having generally solid side wails extending therefrom fordefining a main amplifier cavity with subcavities to contain subcircuitsof the main amplifier subcircuit and an error amplifier cavity withsubcavities to contain subcircuits of the error amplifier subcircuit,the side walls extending to contact the circuit board to isolate thesubcircuits; the lid structure further including a generally soliddividing wall, of greater thickness than the side walls, extendingbetween the main amplifier subcircuit and the error amplifiersubcircuit, the dividing wall having multiple islands extendingtherefrom, the multiple islands passing through multiple cut-outs formedin the circuit board between the main amplifier subcircuit andrespective cavity and error amplifier subcircuit and respective cavityto electrically couple to the chassis body to separate the amplifiercavities and electrically isolate the main and the error amplifiersubcircuits.